Method and apparatus for interlocking tubular members

ABSTRACT

A method and apparatus for interlocking at least one first tube ( 10 ) having a first diametric spacing between opposite points of the tube wall with a second tube ( 4 ) having a second diametric spacing between opposite points of the tube wall which is larger than the first diametric spacing. The first tube is loaded over a mandrel ( 50 ) having a punching end ( 54 ), and disposed into a holding block ( 30 ) having a holding cavity ( 32 ) conforming closely to the outer surface of the first tube. The second tube is disposed over a receiving block ( 40 ), which has a receiving cavity conforming closely to the outer surface of the first tube. The punching end of the mandrel is driven through the second tube and into the cavity in the receiving block, followed by the first tube. When the first tube reaches a lower limit of the receiving cavity, the first tube is compressed axially. The mandrel supports the interior of the first tube, the holding cavity prevents the trailing portion of the first tube from swelling outwardly, and the receiving cavity prevents the leading portion of the first tube from swelling outwardly. Thus, the portion of the first tube disposed inside the second tubular member swells under the axial compressive force, permanently interlocking the first tube with the second tube. The punching steps can be separated from the remaining steps of the method of the invention, or the second tube can be pre-punched. In further embodiments the method and apparatus of the invention can create a clinched interlock and/or a ‘T’-shaped interlocked assembly.

FIELD OF THE INVENTION

This invention relates to the construction of tubular frames. Inparticular, this invention relates to a method and apparatus forinterlocking tubular members without welding.

BACKGROUND OF THE INVENTION

Tubular frames are used in many applications. A tubular frame can beused to form a support for myriad types of materials, for examplesprings, cushions, straps, fabric etc. Although the tubular frame isoften concealed within these other materials, it forms the supportinfrastructure and provides the necessary strength for the finishedarticle.

Many components of an automobile are constructed from one or moretubular frames. In one common example, an automobile seat is constructedby layering springs, cushioning and fabric over a tubular seat frame.The main seat frame is typically bent from a single length of tubing,for example, cylindrical steel tubing. However, a typical seat frameconsists of many tubular subassemblies and components, each of whichmust be affixed to the main seat frame.

The conventional method of affixing a tubular component to anothertubular component, such as a tubular frame, is by welding. Using theexample of an automobile seat frame, in order to affix a headrestsupport to the main seat frame a tubular support post is welded to thetop member of the seat frame.

However, welding is a slow, labour-intensive, inconsistent and dirtyprocess. Further, the welding of parts creates quality control concerns,even when welding is effected by a skilled welder. The effectiveness ofa weld is typically assessed visually, and problems such asburn-through, metal fatigue in the material surrounding the weld,incomplete adhesion due to contaminants on the tubular components and soon, are not always avoidable. In applications such as automobile parts,these types of problems can cause serious safety concerns.

U.S. Pat. No. 6,035,516 entitled “Securement of Head Rest Support intoAutomobile Seat Frame”, issued Mar. 14, 2000 to Petersen, which isincorporated herein by reference, describes a method of securing aheadrest support to a tubular seat frame which presses the tubular seatframe flat at the position of the joint, and utilizes lock-beads swagedinto the headrest support post on either side of the main frame memberto secure the post. Although this process does not involve welding, itis a multi-step process which requires many expensive machinery stagesfor automated production. Also, because the frame is flattened, thetangent points at which the support post contacts the frame are broughtvery close together, so the resistance against torsional stresses isreduced.

It would accordingly be advantageous to provide a method for affixingtubular components to other tubular components without the need forwelding and in a single-step process, while increasing the strength andconsistency of the joints, by removing the element of judgment and othervariables inherent in the welding process.

SUMMARY OF THE INVENTION

The present invention overcomes these disadvantages by providing amethod and apparatus for interlocking tubular members, which isespecially suitable for metal tubes. According to the method of theinvention, a first tubular member (for example a headrest support post)having a first diametric spacing between opposite points of its wall isinterlocked with a second tubular member (for example the main frame ofan automobile seat) having a second diametric spacing between oppositepoints of its wall which is larger than the first diametric spacing. Inthe preferred embodiment this is accomplished in a single operation,thus saving considerable time and cost relative to conventional weldingoperations, and relative to the swaging process described in U.S. Pat.No. 6,035,516, while providing a much stronger connection between theinterlocked components.

The invention accomplishes this by loading the first tubular member overa mandrel having a punching end, and disposing one end of the firsttubular member into a holding block having a holding cavity conformingclosely to the outer surface of the first tubular member. The secondtubular member is disposed in the required orientation (typicallysubstantially perpendicular to the first tubular member) over areceiving cavity in a receiving block, the receiving cavity alsoconforming closely to the outer surface of the first tubular member. Thepunching end of the mandrel and the first tubular member are driventhrough the second tubular member. The mandrel punches through opposedpoints in the wall of the second tubular member and penetrates into thereceiving cavity in the receiving block, followed by the first tubularmember.

When the first tubular member reaches the lower limit of the receivingcavity, an axial compressive force is applied to the first tubularmember. The mandrel supports the interior of the first tubular memberalong substantially its entire length, and thus prevents the firsttubular member from buckling inwardly under the axial compressive force.The holding cavity in the holding block prevents the trailing portion ofthe first tubular member (disposed within the holding cavity) fromswelling outwardly under the axial compressive force. Similarly, thereceiving cavity in the receiving block prevents the leading portion ofthe first tubular member (which has penetrated into the receivingcavity) from swelling outwardly under the axial compressive force.Therefore, the only portion of the first tubular member which can deformunder the axial compression is an interlocking portion, i.e. the portionof the first tubular member disposed inside the second tubular member.The interlocking portion of the first tubular member swells under theaxial compressive force, positively engaging the wall of the firsttubular member against the shoulders created in the wall of the secondtubular member by the punching end of the mandrel. The first tubularmember is thus permanently interlocked with the second tubular member.The interlocked assembly can then be removed from the holding andreceiving blocks and the mandrel withdrawn from the first tubular memberfor further processing.

In the preferred embodiment the lower limit of the receiving cavity isdefined by a tube seat disposed in the receiving cavity, having a hollowend for receiving the punching end of the mandrel. Also, in thepreferred embodiment the second tubular member is clamped in a channelformed between the holding block and the receiving block, substantiallyconforming to the outer surface of the second tubular member, securingthe second tubular member during the interlocking process and ensuringthat only the punched portion of the second tubular member deforms underthe punching force of the mandrel. Optionally a compressive cushion, forexample a nitrogen spring, is disposed in the receiving cavity tofacilitate a controlled compression of the first tubular member.

The holding and receiving blocks in the apparatus of the invention maybe provided with a single holding cavity and receiving cavity,respectively, for interlocking a single tubular member with anothertubular member. In an alternate embodiment the holding and receivingblocks can be respectively provided with multiple holding cavities andreceiving cavities, allowing for the simultaneous interlocking of aplurality of first tubular members with the second tubular member. Ineither embodiment, the apparatus of the invention is easily automatedbecause it is a single-stroke process.

Thus, in one stroke the apparatus of the invention provides a completeand fully secure interlocking engagement between the first and secondtubular members. In effect, the first tubular member is embedded in thesecond tubular member. The protruding shoulder formed by punchingthrough the wall of the second tubular member provides additionalsupport for the joint against torsional forces, and the entrance to thereceiving cavity may be bevelled or chamfered to control the depth andangle of the protruding shoulder.

It will be appreciated that the method and apparatus of the inventioncan be used with any malleable tubing, including without limitationmetal, plastic and other composites. The invention is particularly wellsuited for use with metal tubing, of any desired diameter and having anydesired cross sectional configuration or geometry including, withoutlimitation, round, oval, square, hexagonal etc. The invention can alsobe used to join tubing of different compositions and/or geometries, theonly limitations being that the tubing must be hollow, the wall of thefirst tubular member must be malleable, and the diametric spacingbetween opposite points of the wall of the second tubular member must belarger than or equal to the diametric spacing between opposite points ofthe wall of the first tubular member. Thus, for example, the secondtubular member can be nominally smaller than the first tubular member,but the invention can be applied as long as the second tubular member isflattened so that it has, in one direction, a diametric spacing betweenopposite points of its wall which is larger than or equal to a diametricspacing between opposite points of the wall of the first tubular member.

The holding and receiving cavities and the mandrel body are configuredaccording to the configuration of the tubing, to ensure that the axialcompressive force applied during the interlocking process causes onlythe interlocking portion of the first tubular member to swell. Theinterlocking method according to the invention is much faster and lessexpensive than both welding and swaging techniques, and provides acleaner, more consistent result having a far greater joint strength.

It will also be appreciated that the steps of punching the secondtubular member and driving the first tubular member through the holes inthe second tubular member can be separated. For example, opposed holescan be pre-punched or pre-cut through the wall of the second tubularmember, and the method and apparatus of the invention can be applied toaffix the first tubular member to the second tubular member without thepunching step being involved in the actual securing process.

In further embodiments of the invention the second tubular member may begenerally flattened when the first tubular member is punched through,and beads may be formed in the first tubular member above and/or belowthe wall of the second tubular member. The apparatus for producing thisembodiment is modified to provide spaces into which the wall of thefirst tubular member can expand to form the beads. Also, a ‘T’-shapedinterlocking tube assembly may be formed in accordance with a furtherembodiment of the invention by omitting the receiving cavity so that thefirst tubular member bottoms out on the bottom wall of the secondtubular member.

The present invention thus provides a method of interlocking a firsttubular member having a first diameter with a second tubular memberhaving a second diameter larger than or equal to the first diameter andopposed holes having diameters substantially equal to the diameter ofthe first tubular member, comprising the steps of: a disposing throughthe first tubular member a mandrel having a body with an exteriorsurface substantially conforming to an interior surface of the firsttubular member, to support the interior surface of the first tubularmember; b. disposing a trailing end of the first tubular member within aholding cavity in a holding block, the holding cavity supporting anouter surface of the trailing end; c. driving the a leading end of thefirst tubular member through the wall of the second tubular member andinto a receiving cavity in a receiving block, the receiving cavitysupporting an outer surface of the leading end, until the leading endreaches a lower limit; and d. applying an axial compressive force to thefirst tubular member; whereby an unsupported portion of the firsttubular member contained within the second tubular member swells underthe axial compressive force, interlocking the first tubular member tothe second tubular member.

The present invention further provides a method of interlocking a firsttubular member having a first diameter with a second tubular memberhaving a second diameter larger than or equal to the first diameter,comprising the steps of: a. punching through a wall of the secondtubular member to create opposed holes having diameters substantiallyequal to the diameter of the first tubular member, b. disposing throughthe first tubular member a mandrel having a body with an exteriorsurface substantially conforming to an interior surface of the firsttubular member, to support the interior surface of the first tubularmember; c. disposing a trailing end of the first tubular member within aholding cavity in a holding block, the holding cavity supporting anouter surface of the trailing end; d. driving a leading end of the firsttubular member through the wall of the second tubular member and into areceiving cavity in a receiving block, the receiving cavity supportingan outer surface of the leading end, until the leading end reaches alower limit; and e. applying an axial compressive force to the firsttubular member; whereby an unsupported portion of the first tubularmember contained within the second tubular member swells under the axialcompressive force, interlocking the first tubular member to the secondtubular member.

In further aspects of the method of the invention: the mandrel isprovided with a punching end and the steps of punching through the wallof the second tubular member and driving the a leading end of the firsttubular member through the wall of the second tubular member areperformed in a single stroke; an entrance to the receiving cavity isbevelled; the second tubular member is disposed within a channel havinga configuration conforming to an outer surface of the second tubularmember and extending over an entrance to the receiving cavity; thechannel is formed in the receiving block; the holding block is providedwith a channel conforming to an outer surface of the second tubularmember and extending over an entrance to the holding cavity; the methodincludes, before step a., the step of clamping the holding block againstthe receiving block; the first tubular member is driven through thesecond tubular member by a punch plate to which the mandrel is anchored;and/or the method is used for interlocking a plurality of first tubularmembers with the second tubular member; the lower limit of the receivingcavity is defined by a tube seat.

The invention further provides an apparatus for interlocking at leastone first tubular member having a first diameter with a second tubularmember having a second diameter larger than the first diameter,comprising a holding block having at least one holding cavity forsupporting an outer surface of a trading end of the first tubularmember, a receiving block having at least one receiving cavity disposedin opposition to the holding cavity, for supporting an outer surface ofa leading end of the first tubular member, the receiving cavity having alower limit, at least one mandrel having a body with an exterior surfacesubstantially conforming to an interior surface of the first tubularmember, to support the interior surface of the first tubular member,extending through the holding cavity, and a punch, whereby the punchcreates opposed holes in a wall of the second tubular member, and themandrel and a leading end of the first tubular member are driven throughthe wall of the second tubular member and into the receiving cavity, andwhen the leading end of the first tubular member reaches the lower limitan axial compressive force applied to the first tubular member causes anunsupported portion of the first tubular member contained within thesecond tubular member to swell under the axial compressive force,interlocking the first tubular member to the second tubular member.

In further aspects of the apparatus of the invention: the punch isprovided by a punching end of the mandrel; an entrance to the receivingcavity is bevelled; the second tubular member is disposed within achannel having a configuration conforming to an outer surface of thesecond tubular member and extending over an entrance to the receivingcavity; the channel is formed in the receiving block; the holding blockis provided with a channel conforming to an outer surface of the secondtubular member and extending over an entrance to the holding cavity; atleast one of the holding block and the receiving block are movable andcan be moved toward the other of the holding block and the receivingblock; the mandrel and first tubular member are driven through thesecond tubular member by the punch plate; and/or the apparatus comprisesa plurality of mandrels, holding cavities and receiving cavities forinterlocking a plurality of first tubular members with the secondtubular member; the lower limit of the receiving cavity is defined by atube seat.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate by way of example only a preferredembodiment of the invention,

FIGS. 1A to 1C are schematic perspective views of the first and secondtubular members before, during and after the interlocking method of theinvention, respectively;

FIGS. 2A to 2G are schematic perspective views of the apparatus of theinvention during the stages of the interlocking method of the invention,

FIG. 2H is a cross-sectional perspective view of an interlocked tubeassembly constructed according to a first embodiment of the invention;

FIG. 3 is a perspective view of the punch plate;

FIG. 4 is a perspective view of the mandrel;

FIG. 5 is a perspective view of the holding block;

FIG. 6 is a perspective view of the receiving block;

FIG. 7 is a perspective view of the die button;

FIG. 8 is a perspective view of the tube seat;

FIG. 9 is a cross-sectional perspective view of an interlocked tubeassembly constructed according to a further embodiment of the invention;

FIG. 10 is a cross-sectional perspective view of the apparatus of theinvention for constructing the interlocked tube assembly of FIG. 9;

FIG. 11 is a cross-sectional perspective view of a ‘T’-shapedinterlocked tube assembly constructed according to a further embodimentof the invention; and

FIG. 12 is a cross-sectional perspective view of the apparatus of theinvention for constructing the interlocked tube assembly of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

The principles and operation of the method and apparatus of theinvention will be described in the context of affixing a headrestsupport post 10 (a first tubular member) to a frame member 4 (a secondtubular member) of the main seat frame 2 of an automobile seat (notshown). It will be appreciated that the method and apparatus of theinvention can be equally implemented in numerous other environments,industries and applications, and the following description in theenvironment of an automobile seat frame is merely an illustrativeexample.

The components of the apparatus 20 of the invention are illustrated inFIGS. 3 to 8. In the preferred embodiment the apparatus 20 comprises aholding block 30 comprising at least one holding cavity 32; a receivingblock 40 comprising at least one receiving cavity 42, disposed inopposition to the holding cavity 32; for each set of holding/receivingcavities 32, 42, a mandrel 50 having an anchored end 52 and a punchingend 54 with a punch 56; a punch plate 60 to which the mandrels 50 areanchored; and for each mandrel 50 a tube seat 70 anchored to a seatplate 80.

The holding block 30 is preferably provided with a channel 34 extendingover the holding cavities 32, configured to substantially conform to theouter wall of the frame member 4. Similarly, the receiving block 40 ispreferably provided with a channel 44 extending over the receivingcavities 42, also configured to substantially conform to the outer wallof the frame member 4. In the embodiment shown the channels 34, 44 areeach semi-circular in cross-section, to thus closely conform to thecylindrical outer surface of the frame member 4 when the holding andreceiving blocks 30, 40 are clamped together. This holds the framemember 4 securely in place during the interlocking process, and resistsflattening of the frame member 4 under the compressive force imparted bythe punching end 54 of the mandrel 50. The holding block 30 andreceiving block 40 are mounted in opposition, preferably so that theycan be moved toward and away from each other for loading the supportposts 10 onto the mandrels 50, and for clamping the frame member 4 intoposition for interlocking.

Each mandrel 50 has a body 58 configured with a close tolerance to theinner wall of the support post 10, which in the embodiment shown iscylindrical, and extends substantially the entire length of the supportpost 10. The anchoring ends 52 of the mandrels 50 are anchored to thepunch plate 60, for example bolted, in anchoring recesses 62. Themandrels 50 are positioned on the punch plate 60 such that the mandrels50 slidably extend through openings (not shown) into the holdingcavities 32. The punching ends 54 of the mandrels 50 thus can be movedto protrude out of the holding cavities 32 and penetrate through theframe member 4 and into the receiving cavities 42 during theinterlocking operation.

Preferably a tube seat 70, for example a die button having a hollow endfor receiving the punching end 54 of the mandrel 50, is disposed withineach receiving cavity 42, anchored to a seat plate 80. The tube seats 70are each provided with an opening 72 facing the punching end 54 of thecorresponding mandrel 50, forming a punch seat 74 into which thepunching end 54 can nest without damaging the punch 56. The rim 76 ofthe tube seat 70 forms a lower limit of the path of travel of thesupport post 10, as described below.

It will be appreciated that the tube seats 70 and seat plate 80 can beformed as an integral unit if desired. Also, the use of a separate tubeseat 70 facilitates changing the lower limit of the receiving cavity 42,for example to accommodate a different length of support post 10, bymerely switching to a tube seat 70 of a different length. However, thelower limit can instead be formed within the receiving cavity 42 itself,for example as a ledge milled into the cavity wall, although this isless convenient as it would require changing the entire receiving block40 in order to accommodate a different length of support post 10.

All of the components of the apparatus are composed of a strong, rigidmaterial, for example hardened steel, in order to withstand the stressesof the interlocking operation without substantial deformation ordeterioration. The apparatus 20 may be actuated by any suitablereciprocating device (not shown), for example a motor, solenoid,hydraulic or pneumatic piston, etc. Electrical actuators are preferred,as they ordinarily provide faster cycle intervals.

The apparatus 20 of the invention has been described and illustratedusing an embodiment arranged to simultaneously interlock two supportposts 10 to the frame member 4. It will be appreciated that theapparatus 20 can be designed to interlock a single support post 10 tothe frame member 4, or to interlock more than two support posts 10 tothe frame member 4, depending solely upon the number of holding andreceiving cavities 32, 42 respectively provided in the holding andreceiving blocks 30, 40, each with an associated punching mandrel 50,and with the appropriate compressive force applied to deform multiplesupport posts 10.

Further, the apparatus of the invention has been described using tubularmembers 4 and 10 which each have generally circular cross-sections, inwhich case the frame member 4 must have a diameter which is larger thanor equal to the diameter of the support posts 10, so that the secondtubular member has a diametric spacing between opposite points of itswall (in this case, any diameter) which is larger than or equal to adiametric spacing between opposite points of the wall of the firsttubular member. However, as noted above, the invention can beimplemented if the support posts 10 were nominally larger than the framemember 4, as long as the frame member 4 is flattened so that it has, inone direction, a diametric spacing between opposite points of its wallwhich is larger than a diametric spacing between opposite points of thewall of the support posts 10.

The operation of the invention will be described in relation to apreferred embodiment of the method of the invention, illustrated inFIGS. 2A to 2G. The mandrels 50 are inserted through the holding block30, and the headrest support posts 10 are loaded onto the mandrels 50with their trailing ends 10 a inserted into the holding cavities 32, asshown in FIG. 2A. The frame member 4 is loaded into the channel 44 inthe receiving block 40, as shown in FIG. 2B. FIG. 2C illustrates across-section of the apparatus with the support posts 10 and framemember 4 loaded for interlocking. The holding block 30 and receivingblock 40 are then clamped together, securing the frame member 4 inposition, as shown in FIG. 2D.

The punch plate 60 is driven toward the holding block 30 by an actuator(not shown), which in turn drives the mandrels 50 through opposed sidesof the wall of the frame member 4 and forces the leading ends 10 b ofthe support posts 10 through the openings punched through the wall ofthe frame member 4, until the leading ends 10 b of the support posts 10strike the rims 76 of the tube seats 70. At this stage the support posts10 are in the correct within the frame member 4 for interlocking, andthere remains a small clearance or gap between the punch plate 60 andthe holding block 30, as shown in FIG. 2E. In the preferred embodimentthere is also a small clearance or gap between the seat plate 80 and thereceiving block 40, as shown in FIG. 2E.

With the support posts 10 abutting the lower limit of the receivingcavities 42, defined by the rims 76 of the tube seats 70, as the punchplate 60 is driven into contact with the holding block 30 (as shown inFIG. 2F) the seat plate 80 is brought into contact with the receivingblock 40 and the support posts 10 are thus axially compressed, becausethe tube seats 70 block the leading ends 10 b of the support posts 10from moving further into the receiving cavities 40. It will beappreciated that the punch seat 74 must extend sufficiently deep withinthe hollow end of the tube seat 70 that the punching end 54 of themandrel 50 does not contact the punch seat 74 before the punch plate 60contacts the holding block 30, to ensure that the mandrel 50 does notresist the axial compressive force applied to deform the support post10.

The body 58 of the mandrel 50 supports the interior surface of thesupport post 10 and prevents the support post 10 from buckling inwardlyunder the axial compressive force. The holding and receiving cavities32, 42 respectively support the outer surface of the support post 10.Thus, the holding cavity 32 prevents the trailing end 10 a of thesupport post 10 from swelling outwardly under the axial compressiveforce, and the receiving cavity 42 prevents the leading end 10 b of thesupport post 10 from swelling outwardly under the axial compressiveforce. Therefore, the only unsupported portion of the wall of thesupport post 10 is the outer wall of the interlocking portion 12, whichis the portion of the support post 10 disposed inside the frame member4. The interlocking portion 12 thus swells under the axial compressiveforce, positively engaging the wall of the support post 10 against theshoulders 4 a, 4 b created in the tube wall by the punching end 54 ofthe mandrel 50 (best seen in FIG. 2H). The entrance to the receivingcavity 42 may be bevelled or chamfered, as at 42 a, to control the depthand angle of the protruding shoulder 4 b.

Following the application of axial compressive force the support post 10cannot be moved axially relative to the tubular member 4, because theswollen interlocking portion 12 is larger than the openings in the wallof the frame member 4. The swollen interlocking portion 12 of thesupport post 10 positively engages against the shoulders 4 a, 4 b formedin wall of the frame member 4, providing resistance to rotational andtorsional forces. The support posts 10 are thus permanently interlockedwith the frame member 4. The holding and receiving blocks 30, 40 arethen drawn apart, withdrawing the mandrels 50 from the support posts 10as shown in FIG. 2G, and the interlocked assembly (shown in FIG. 2H) canbe removed from the receiving block 40 for further processing.

Thus, in a single stroke the apparatus 20 of the invention can provide acomplete and fully secure interlocking engagement between the supportposts 10 and frame member 4, without welding and without the need toswage or affix extraneous components to secure the joint.

To effect the steps of punching through the wall of the frame member 4and driving the a leading end of the support post 10 through the wall ofthe frame member 4 in a single stroke, the mandrel 50 is provided with apunching end 54. However, it will be appreciated that in an alternativeembodiment the steps of punching through the wall of the frame member 4and driving the a leading end of the support post 10 through the wall ofthe frame member 4 can be effected in two separate operations, in whichcase the mandrel 50 need only be configured to support the interior wallof the support post 10. Although the wall of the frame member 4 must bepunched before the support post 10 is driven through the frame member 4,the support post 10 can be loaded on the mandrel 50 and into the holdingblock 30 either before or after the punching step. This two-strokemethod is somewhat less efficient, but the principles of the inventionapply equally and the resulting joint would be comparable to thesingle-stroke method described above.

As noted above, the steps of punching the frame member 4 and driving thesupport post 10 through the frame member 4 can be separated. Forexample, opposed holes can be pre-punched or pre-cut through the wall ofthe frame member 4, and the method and apparatus of the invention can beused to affix the support post 10 to the frame member 4 in the mannerdescribed above.

It is also possible to punch through the frame member 4 so that aprotruding shoulder 4 a is created exterior to both of the opposedholes. This is accomplished by piercing through the frame member 4 tocreate small holes at the desired position; positioning a ball bearingor other like element of the required diameter (i.e. the diameter of thesupport post 10) inside the frame member 4 at the position of the holes;driving the ball bearing through one of the holes from inside the framemember 4; repositioning the ball bearing or other like element insidethe frame member 4 at the position of the holes; and driving the ballbearing through the other of the holes from inside the frame member 4.This provides the advantage of greater distance between the tangentpoints, which in turn provides greater support for the joint.

In the embodiment described above, the tube seat 70 is lodged in astationary position within the receiving cavity 42. Optionally acompressive cushion, for example a nitrogen spring (not shown), isdisposed in the receiving cavity 42 beneath the tube seat 70, so thatthe tube seat 70 is initially raised in the receiving cavity 42, and asthe mandrel punches through the tubular member 4 and enters into thereceiving cavity 42, the tube seat 70 is pushed through the receivingcavity 42 as the holding block 30 is clamped to the receiving block 40.This may facilitate a more controlled compression of the support post10.

As shown in FIG. 2F, the holding and receiving cavities 32, 42 mayoptionally be provided with annular cavities 32 a, 42 a immediatelyabove and below the position of the frame member 4 (allowing clearancefor the shoulder 4 a). In this embodiment, when axially compressed thesupport post 10 expands into the annular cavities 32 a, 42 a to createdswage rings 10 a, 10 b, for additional support.

In the preferred embodiment described above, the frame member 4 isclamped within the tubular channel formed by the channel 34 in theholding block 30 and the channel 44 formed in the receiving block 40.This retains the frame member 4 in position and helps to ensure thatonly the punched portion of the frame member 4 deforms under thepunching force of the mandrel 50. However, it will be appreciated thatother means can be used for retaining and supporting the frame member 4during the interlocking process.

Although the preferred embodiment of the invention so described andillustrated is adapted for interlocking two support posts 10 with theframe member 4, the holding and receiving blocks 30, 40 may be providedwith a single holding cavity 32 and receiving cavity 42, respectively,for interlocking a single support post 10 with the frame member 4, orthe holding and receiving blocks 30, 40 can be respectively providedwith any desired additional number of holding cavities 32 and receivingcavities 42, allowing for the simultaneous interlocking of any number ofsupport posts 10 with the frame member 4.

FIG. 9 illustrates a further embodiment of the invention that providesparticularly strong resistance to rotation of the first tubular member110 (e.g. a support post) in the second tubular member 104 (e.g. a framemember). The second tubular member 104 is generally flattened when thefirst tubular member 110 is punched through, and beads 110 a, 110 b areformed in the first tubular member 110 against both the interior and theexterior the wall of the second tubular member 104.

The apparatus for producing this embodiment is shown in FIG. 10, inwhich the holding block 130 comprises at least one holding cavity 132having a recess 131 which provides a space into which the wall of thefirst tubular member 110 expands to form the bead 110 a; the recess 131being formed about a mouth 133 which flattens the second tubular member104 during compression. Likewise, the receiving block 140 comprises atleast one receiving cavity 142, disposed in opposition to the holdingcavity 132, having a recess 141 which provides a space into which thewall of the first tubular member 110 expands to form the bead 110 b; andthe recess 141 is formed about a mouth 143 which flattens the secondtubular member 104 during compression.

As long as equal force is applied to each end of the first tubularmember 110 during the compression stage, the beads 110 a, 110 b willform substantially equally and will clinch the wall of the secondtubular member 104 tightly to resist both axial dislodgement of thefirst tubular member 110 from the second tubular member 104 and rotationof the first tubular member 110 within the second tubular member 104. Inthis embodiment, the extent of expansion of the wall of the firsttubular member 110 inside the second tubular member 104 is limitedbecause the second tubular member 104 is flattened during thecompression process. The size of the beads 110 a,110 b can be controlledby a combination of the size of the recesses 131, 141 and the length ofthe compression stroke. This embodiment of the invention otherwiseoperates as described above.

FIG. 11 illustrates a ‘T’-shaped interlocking tube assembly, formed inaccordance with a further embodiment of the invention. In thisembodiment, shown in FIG. 12, the receiving block 240 does not have areceiving cavity. The leading end of the first tubular member 210bottoms out on the bottom wall of the second tubular member 204, whichserves as a tube seat (supported by the channel 244, to preventdeformation of the wall of the second tubular member 204), and theapplication of a compressive force by the punch plate 260 swells thefirst tubular member 210 in the manner described above. This embodimentof the invention otherwise operates as described above, with or withouta bead 210 a.

Various embodiments of the present invention having been thus describedin detail by way of example, it will be apparent to those skilled in theart that variations and modifications may be made without departing fromthe invention. The invention includes all such variations andmodifications as fall within the scope of the appended claims.

1. A method of interlocking a first tubular member having a firstdiametric spacing between opposite points of a wall of the first tubularmember with a second tubular member having a second diametric spacingdiametric spacing between opposite points of a wall of the first tubularmember which is larger than or equal to the first diametric spacing,comprising the steps of: a. punching through a wall of the secondtubular member to create opposed holes each having a diametric spacingbetween opposite points of an edge of the hole substantially equal tothe diametric spacing of the first tubular member, b. disposing throughthe first tubular member a mandrel having a body with an exteriorsurface substantially conforming to an interior surface of the firsttubular member, to support the interior surface of the first tubularmember; c. disposing a trailing end of the first tubular member within aholding cavity in a holding block, the holding cavity supporting anouter surface of the trailing end; d. driving a leading end of the firsttubular member through the wall of the second tubular member and into areceiving cavity in a receiving block, the receiving cavity supportingan outer surface of the leading end, until the leading end reaches alower limit; and e. applying an axial compressive force to the firsttubular member; whereby an unsupported portion of the first tubularmember contained within the second tubular member swells under the axialcompressive force, interlocking the first tubular member to the secondtubular member.
 2. The method of claim 1 wherein the mandrel is providedwith a punching end and the steps of punching through the wall of thesecond tubular member and driving the leading end of the first tubularmember through the wall of the second tubular member are performed in asingle stroke.
 3. The method of claim 1 wherein an entrance to thereceiving cavity is bevelled.
 4. The method of claim 1 wherein thesecond tubular member is disposed within a channel having aconfiguration conforming to an outer surface of the second tubularmember and extending over an entrance to the receiving cavity.
 5. Themethod of claim 4 wherein the channel is formed in the receiving block.6. The method of claim 5 wherein the holding block is provided with achannel conforming to an outer surface of the second tubular member andextending over an entrance to the holding cavity.
 7. The method of claim6 including, before step a, the step of clamping the holding blockagainst the receiving block.
 8. The method of claim 7 wherein the firsttubular member is driven through the second tubular member by a punchplate to which the mandrel is anchored.
 9. The method of claim 1 forinterlocking a plurality of first tubular members with the secondtubular member.
 10. The method of claim 1 wherein the lower limit of thereceiving cavity is defined by a tube seat.
 11. A method of interlockinga first tubular member having a first diametric spacing between oppositepoints of a wall of the first tubular member with a second tubularmember having a second diametric spacing between opposite points of awall of the second tubular member which is larger than or equal to thefirst diametric spacing, and opposed holes each having a diametricspacing diametric spacing between opposite points of an edge of the holesubstantially equal to the diametric spacing of the first tubularmember, comprising the steps of: a. disposing through the first tubularmember a mandrel having a body with an exterior surface substantiallyconforming to an interior surface of the first tubular member, tosupport the interior surface of the first tubular member; b. disposing atrailing end of the first tubular member within a holding cavity in aholding block, the holding cavity supporting an outer surface of thetrailing end; c. driving the a leading end of the first tubular memberthrough the wall of the second tubular member and into a receivingcavity in a receiving block, the receiving cavity supporting an outersurface of the leading end, until the leading end reaches a lower limit;and d. applying an axial compressive force to the first tubular member;whereby an unsupported portion of the first tubular member containedwithin the second tubular member swells under the axial compressiveforce, interlocking the first tubular member to the second tubularmember.
 12. The method of claim 1 comprising, before the step of drivinga leading end of the first tubular member through the wall of the secondtubular member, the step of punching through a wall of the secondtubular member.
 13. The method of claim 11 wherein the mandrel isprovided with a punching end and comprising, simultaneously with thestep of driving a leading end of the first tubular member through thewall of the second tubular member, the step of punching through a wallof the second tubular member.
 14. An apparatus for interlocking at leastone first tubular member having a first diametric spacing betweenopposite points of a wall of the first tubular member with a secondtubular member having a second diametric spacing between opposite pointsof a wall of the second tubular member which is larger than the firstdiametric spacing, comprising a holding block having at least oneholding cavity for supporting an outer surface of a trailing end of thefirst tubular member, a receiving block having at least one receivingcavity disposed in opposition to the holding cavity, for supporting anouter surface of a leading end of the first tubular member, thereceiving cavity having a lower limit, at least one mandrel having abody with an exterior surface substantially conforming to an interiorsurface of the first tubular member, to support the interior surface ofthe first tubular member, extending through the holding cavity, and apunch, whereby the punch creates opposed holes in a wall of the secondtubular member, and the mandrel and a leading end of the first tubularmember are driven through the wall of the second tubular member and intothe receiving cavity, and when the leading end of the first tubularmember reaches the lower limit an axial compressive force applied to thefirst tubular member causes an unsupported portion of the first tubularmember contained within the second tubular member to swell under theaxial compressive force, interlocking the first tubular member to thesecond tubular member.
 15. The apparatus of claim 14 wherein the punchis provided by a punching end of the mandrel.
 16. The apparatus of claim14 wherein an entrance to the receiving cavity is bevelled.
 17. Theapparatus of claim 14 wherein the second tubular member is disposedwithin a channel having a configuration conforming to an outer surfaceof the second tubular member and extending over an entrance to thereceiving cavity.
 18. The apparatus of claim 17 wherein the channel isformed in the receiving block.
 19. The apparatus of claim 18 wherein theholding block is provided with a channel conforming to an outer surfaceof the second tubular member and extending over an entrance to theholding cavity.
 20. The apparatus of claim 19 wherein at least one ofthe holding block and the receiving block are movable and can be movedtoward the other of the holding block and the receiving block.
 21. Theapparatus of claim 14 wherein the mandrel and first tubular member aredriven through the second tubular member by the punch plate.
 22. Theapparatus of claim 14 comprising a plurality of mandrels, holdingcavities and receiving cavities for interlocking a plurality of firsttubular members with at least one second tubular member.
 23. Theapparatus of claim 14 wherein the lower limit of the receiving cavity isdefined by a tube seat.
 24. A method of interlocking a first tubularmember having a first diametric spacing between opposite points of awall of the first tubular member with a second tubular member having asecond diametric spacing diametric spacing between opposite points of awall of the first tubular member which is larger than or equal to thefirst diametric spacing, comprising the steps of: a. punching through awall of the second tubular member to create a hole having a diametricspacing between opposite points of an edge of the hole substantiallyequal to the diametric spacing of the first tubular member, b. disposingthrough the first tubular member a mandrel having a body with anexterior surface substantially conforming to an interior surface of thefirst tubular member, to support the interior surface of the firsttubular member; c. disposing a trailing end of the first tubular memberwithin a holding cavity in a holding block, the holding cavitysupporting an outer surface of the trailing end; d. driving a leadingend of the first tubular member through the wall of the second tubularmember and against a diametrically opposed point of the wall of thesecond tubular member, e. supporting the diametrically opposed point ofthe wall of the second tubular member to thus create a lower limit forthe leading end of the first tubular member; and f. applying an axialcompressive force to the first tubular member; whereby an unsupportedportion of the first tubular member contained within the second tubularmember swells under the axial compressive force, interlocking the firsttubular member to the second tubular member.
 25. The method of claim 24wherein the mandrel is provided with a punching end and the step ofpunching through the wall of the second tubular member and driving theleading end of the first tubular member through the wall of the secondtubular member are performed in a single stroke.
 26. The method of claim24 wherein the second tubular member is disposed within a channel havinga configuration conforming to an outer surface of the second tubularmember to support the diametrically opposed point of the wall of thesecond tubular member.
 27. The method of claim 26 wherein the channel isformed in the receiving block.
 28. The method of claim 27 wherein theholding block is provided with a channel conforming to an outer surfaceof the second tubular member and extending over an entrance to theholding cavity.
 29. The method of claim 28 including, before step a, thestep of clamping the holding block against the receiving block.
 30. Themethod of claim 29 wherein the first tubular member is driven throughthe second tubular member by a punch plate to which the mandrel isanchored.
 31. The method of claim 24 for interlocking a plurality offirst tubular members with the second tubular member.